GENERALIZED
CELL
Principle parts
1-plasma
membrane
2-cytoplasm
3-nucleus
Lipid bilayer
Fluid mosaic
model: The
membrane
resembles a
continually moving
sea of lipids that
contains a
“mosaic” of many
different proteins.
Types of lipid
molecules
1- Phospholipids: 75
%
2-cholesterol
molecules: 20 %
3- Glycolipids: 5 %
Membrane proteins
1-Integral proteins extend into or through the lipid bilayer and are
firmly embedded in it. Most integral proteins are (transmembrane
proteins)
2-Peripheral proteins: attached to membrane lipids or integral
proteins at the inner or outer surface of the membrane.
Cytoplasm
Cytosol and organelles
Cytosol
55 % of total cell volume
75–90 % of cytosol is water plus various dissolved and
suspended components
Cytoskeleton: Network of protein filaments that extends
throughout the cytosol
Three types according to diameter:
Microfilaments
Intermediate filaments
Microtubules
Microfilaments
The thinnest type
Composed of the proteins actin
and myosin
Functions:
Movement: muscle
contraction, cell division, and
cell locomotion i.e. migration of
embryonic cells during
development, WBC invasion to
fight infection, and migration of
skin cells during wound healing.
Mechanical support:
anchoring the cytoskeleton to
integral proteins, supports
microvilli (nonmotile,
microscopic (fingerlike
projections of the plasma
membrane) i.e. epithelial cells
that line the small intestine.
Intermediate filaments
Thicker than
microfilaments
Different strong
proteins can
compose
intermediate
filaments.
Functions
1) anchoring organelles
such as nucleus.
2) attach cells to one
another.
Microtubules
The largest of the
cytoskeletal
components,
Long, unbranched
hollow tubes made of
tubulin.
Functions
1) migration of
chromosomes during
cell division
2) movement of
specialized cell
projections such as cilia
and flagella.
Organelles:
Centrosome
The centrosome:
near the nucleus.
(Two components)
1) Centrioles
cylindrical
structures, each
composed of nine
clusters of three
microtubules
(triplets) arranged in
a circular pattern
2) Pericentriolar
material: ringshaped complexes
composed of the
protein tubulin.
Function:
tubulin complexes are the organizing centers for growth of the
mitotic spindle, important for cell division.
Cilia
Cilia: numerous, short, motile hairlike projections of
the cell surface.
Cilia
Structure:
a core of 20
microtubules
surrounded by
plasma
membrane
arranged with one
pair in the center
surrounded by
nine doublets
(clusters of two
fused
microtubules).
anchored to a
basal body.
Example:
cilia of the
respiratory tract
cells, uterine tube.
Flagella
Structure: similar to
cilia but are typically
much longer, usually
move an entire cell.
Example: flagellum
of the sperm cell
(tail), which moves
the sperm toward
the oocyte in the
uterine tube.
Ribosomes
Ribosomal
RNA (rRNA)
and many
ribosomal
proteins.
Structure:
consists of two
subunits, one
about half the
size of the
other. The two
subunits are
made
separately in
the nucleolus.
Produced in
the nucleus
become
functional in
the cytosol.
Types and Functions:
1) Membrane bound ribosomes: associated with
endoplasmic reticulum synthesize proteins destined
for insertion in the plasma membrane or secretion
from the cell.
2) Free ribosomes synthesize proteins used in the
cytosol.
Endoplasmic Reticulum
Flattened sacs or
tubules extends from
the nuclear envelope
which it is connected,
throughout the
cytoplasm.
Rough ER: studded
with ribosomes,
synthesizes
glycoproteins and
phospholipids that are
transferred into cellular
organelles, inserted into
the plasma membrane,
or secreted during
exocytosis.
Smooth ER: synthesizes fatty acids and steroids, such as estrogens
and testosterone; inactivates or detoxifies drugs and other potentially
harmful substances; and stores and releases calcium ions that trigger
contraction in muscle cells.
Golgi Complex
Consists of 3 to
20 cisternae
(small,
flattened
membranous
sacs (curved
cup shape).
Structures of
the cisternae
1)Cis face
2)medial
cisternae
3)Trans face
Functions: Processing, sorting and packaging of synthesized
proteins by ribosomes.
Lysosomes
Structure: membrane-enclosed vesicles that form from
the Golgi complex, contain up to 60 kinds of powerful
digestive enzymes.
Functions:
1. Digest substances entering cell by endocytosis
2. Autophagy: digestion of worn-out organelles.
3. Autolysis: the digestion of the entire cell (tissue
deterioration immediately after death).
4. Extracellular digestion. Enzymes from lysosomes in
the head of a sperm cell ( support penetration).
Peroxisomes
similar in structure to lysosomes but smaller.
abundant in the liver.
oxidases, enzymes that can oxidize (remove
hydrogen atoms), oxidize toxic substances,
such as alcohol.
catalase, which decomposes H2O2.
peroxisomes protect other parts of the cell
from the toxic effects of H2O2.
Mitochondria: structure
Mitochondria
ATP production through aerobic (oxygen
requiring) respiration (powerhouses)
Abundant in tissues of high energy
requirement (Muscle, liver and kidney)
Important for apoptosis (programmed cell
death.
self-replicating, mitochondrial genes are
inherited from the maternal parent (mother
oocyte)
Nucleus
Spherical or oval-shaped structure that usually is the most
prominent feature of a cell.
nuclear envelope: A double membrane that separates the nucleus
from the cytoplasm.
Nucleus
Nuclear pores: control the movement of substances between the
nucleus and the cytoplasm.
Nucleolus: cluster of protein, DNA, and RNA that is not enclosed by
a membrane. (producing ribosomes).
Chromosomes: Genes arrangement (hereditary units).
CELL JUNCTIONS
Cell junctions are contact points between
the plasma membranes of tissue cells.
1) Tight junctions
2) Adherens junctions
3) Desmosomes
4) Hemidesmosomes
5) Gap junctions
Tight junctions
Weblike strands of
transmembrane
proteins that fuse
together the outer
surfaces of adjacent
plasma membranes to
seal off passageways
between adjacent
cells.
inhibit the passage of
substances between
cells and prevent the
contents of these
organs from leaking
into the blood or
surrounding tissues.
Example: Cells of epithelial tissues that line the stomach, intestines, and
urinary bladder.
Adherens junctions
Plaque: dense layer
of proteins on the
inside of the plasma
membrane that
attaches both to
membrane proteins
and to
microfilaments of the
cytoskeleton.
Cadherins:
Transmembrane
glycoproteins join the
cells. Each cadherin
inserts into the plaque
from the opposite side
of the plasma
membrane, and
connects to a
cadherin of an
adjacent cell.
adherens junctions form extensive zones called adhesion belts
Adherens junctions help epithelial surfaces resist separation during
various contractile activities (food movement).